This invention relates to bipolar electrosurgical instruments.
Some surgical procedures (such as severe retinal detachment repair and diabetic retinopathy) require the surgeon to insert surgical instruments into the posterior chamber of the eye. Because the eye should be maintained at a relatively constant pressure during the procedure, tubing to which fluid is applied from an elevated (such as by 2-3 feet) irrigation fluid bottle is inserted through the sclera, and the internal eye pressure is controlled by adjusting the height of the bottle.
The need for tightly controlling eye pressure dictates that the surgical instruments be as small as possible in cross-sectional diameter (to minimize leakage around the instruments and limit fluid loss during exchange of the instruments). Accordingly, an informal "standard" has evolved that surgical instruments used in the posterior eye chamber either be made from 20 gauge hypodermic tubing (which is 0.0355 inches in diameter) or be capable of passing through and sealing an opening equivalent to that created by a 20 gauge needle.
Frequent exchanges of the instruments tend to enlarge the puncture and increase fluid leakage, and are also frustrating for the surgeon and time consuming. It thus is desirable to design instruments which can perform multiple tasks. As the complexity of surgical procedures performed in the posterior chamber of the eye increases, the need for additional, intricate instruments increases as well. Basing the size of such instruments on the 20 gauge "standard" severely limits design options. (The need for limiting the size of the bore created by a surgical instrument and minimizing the number of instrument exchanges is not limited to ocular surgery--these goals also exist in other procedures, such as endoscopy and microsurgery on other areas of the body, such as the brain.)
Most extensive posterior surgery requires controlling hemorrhaging, which typically is done using bipolar radio frequency (RF) coagulation. In one coagulation method, two conductive instruments that are otherwise in use in the eye (e.g., an aspiration tube and a metal jacket of a fibre optic light source) are brought close together near the bleeding vessel while applying RF energy to the instruments. Current conducts in the region of closest spacing between the instruments and coagulates the vessel.
As an alternative, coaxial bipolar electrosurgical instruments (such as that described in U.S. Pat. No. 4,548,207, entitled "Disposable Coagulator," assigned to the present assignee and incorporated herein by reference) have been developed. In a coaxial bipolar instrument, an insulated wire is installed within a metal hypodermic tube, thereby providing a pair of electrodes whose distal tips are exposed and closely spaced to support current conduction therebetween. The exposed area limits the extent of the coagulation, which is advantageous in posterior chamber surgery. variations on bipolar instruments include replacing the wire with an inner tube, which allows the instrument to be used for aspiration as well as coagulation.